1. Field of the Invention
The invention relates to a device for treating growing, dilated or malformed blood vessels with a laser which emits radiation in a wavelength range from 750 nm to 850 nm.
2. Description of the Related Art
WO 97/31582 has already disclosed the treatment of, for example, tumors by administering to the patient a dye or chromophore having an absorption maximum in a wavelength range from 770 nm to 840 nm, and treating the diseased area of the body with light having a wavelength in the stated range. Indocyanine green is proposed as dye or chromophore. A diode laser is a preferred light source.
U.S. Pat. No. 5,394,199 discloses the production of angiographic images of the capillary network of the eye (choriocapillaris) using indocyanine green in order to use them for precise adjustment of the therapeutic laser.
xe2x80x9cOphthalmic Surgeryxe2x80x9d, March 1994, Vol. 25, No. 3, pages 195-201 discloses the selective removal of choroidal neovascular membranes with administration of ICG and treatment with a diode laser having an emission wavelength of 805 nm.
U.S. Pat. No. 5,304,170 discloses the destruction of carotene-containing body tissue with a laser with an emission wavelength of 504 nm. It is provided for this purpose to increase the carotene content by administering carotene.
U.S. Pat. No. 5,071,417 discloses an apparatus for fusion of biological material using a laser. Since the progress of such a fusion is often difficult to observe with the naked eye, the apparatus is equipped with a reflectance monitor which establishes the change in the reflectance characteristics of the tissue material caused by the fusion and thus indicates the success of the fusion to the therapist.
WO 91/18646 discloses a device for laser photothermotherapy. In the disclosed device, tissue which contains endogenous or exogenous chromophore is irradiated with a laser. The temperature of the treated tissue is measured, and the measured signal is used to control the pulse energy and the rate of repetition of the laser pulses.
WO 93/03793 discloses a medical light treatment apparatus, in particular for acupuncture. With the apparatus, the light reflected by the biological tissue is detected and, on the basis of this detection, the energy of the light directed into the tissue is controlled.
In summary, concerning the prior art discussed above it can be stated that most known devices are not intended and not suitable for treating blood vessels, in particular for treating small blood vessels (spider veins). The known devices chiefly make use of endogenous chromophores such as, for example, hemoglobin for absorbing the laser light. The problem which therefore arises on treatment of blood vessels is that vessels which are too small contain too little hemoglobin whereas blood vessels which are too large cannot, because of the poor absorption properties of hemoglobin and the increased heat convection, be heated sufficiently and thus in both cases a sufficient thermal effect with subsequent coagulation of the vessel is not achieved.
The invention is by contrast based on the object of providing a device for treating growing, dilated or malformed blood vessels with a laser, which is distinguished in that the blood vessels are effectively coagulated and adverse effects on the surrounding tissue are minimal. It is further object of this invention to provide a method for treating biological material with a light beam.
These objects are achieved according to the invention with a device and a method for treating growing, dilated or malformed blood vessels with a laser which emits radiation in a wavelength range from 750 nm to 850 nm and which has a measuring unit which measures the concentration of an exogenous chromophore which absorbs the laser beam in a blood vessel to be treated, and which also has a control unit which controls the power of the laser in a contrary sense to the measured concentration. The measurement according to the invention of the concentration of an exogenous chromophore, i.e. chromophone which has been administered to the patient, and the corresponding control of the laser power makes it possible to meter the laser power optimally. As long as the concentration of the exogenous chromophore in the blood vessel to be treated is high, a lower laser power is sufficient. If over the course of time, as a consequence of the breakdown or excretion of the exogenous chromophore from the blood circulation, the concentration thereof falls, in the device according to the invention the power of the laser is controlled in the contrary sense, i.e. increased. It may be pointed out in this connection that power means the energy per unit time (with watt as unit of measurement) introduced into the vessel by the treatment.
The concentration of the exogenous chromophore in the blood vessel can be measured in a variety of ways, for example also by taking a blood sample.
However, a particularly advantageous measuring unit is designed as a reflection measuring unit because this operates non-invasively and is accordingly associated with less stress for the patient. A certain fraction of the laser light which impinges on the surface of the skin is, owing to the different refractive indices of air and skin, reflected (reflection coefficient R).
P1 is P0xe2x88x92RP0=P0(1xe2x88x92R)
where P1 is the reflected and P0 is the originally emitted power. The fraction P2 of the original power P0 which arrives, after passing through the epidermis and part of the dermis, at the blood vessel emerges from the following formula:
P2=P1 exp(xe2x88x92xcex1mel(xcex)z)xe2x88x92P1RH=P1[exp(xe2x88x92xcex1Mel(xcex)z)xe2x88x92RH]
P2=P0(1xe2x88x92R)[exp(xe2x88x92xcex1MEL(xcex)z)xe2x88x92RH}].
In this, the factor xcex1H(xcex)z describes the attenuation of the laser light in the direction of propagation z from the surface of the skin until the particular blood vessel is reached. The factor xcex1Mel(xcex)z depends on the melanin content of the particular section of skin. The absorption, mediated by the chromophore concentration, of the laser light of power P is thus
P=P2(1xe2x88x92T)
P=P0(1xe2x88x92R)[exp(xe2x88x92xcex1Mel(xcex)z)xe2x88x92RH][1xe2x88x92exp(xe2x88x92xcex1CH((xcex,t)z)]
The attenuation of the laser light by the reflection R, the internal reflection RH and by the factor exp(xe2x88x92xcex1Mel(xcex)z) does not, in contrast to the chromophore concentration xcex1CH(xcex,t), vary with time. It is possible by measuring the reflected proportion of the incident light to determine, by the above calculation, the changing chromophore concentration in the blood vessel (xcex1CH((xcex,t)). The control unit controls, on the basis of the measured chromophore concentration, the power of the laser in the contrary sense to the measured concentration, i.e. the power of the laser is set at a comparatively low level when the concentration is high, whereas a comparatively high laser power is applied when the concentration is relatively low.
Another advantageous embodiment of the invention provides for the control unit, in order to measure the concentration of the chromophore, to cause a pilot light pulse to be emitted, the power of which is so small that it causes no permanent changes in the blood vessel or the tissue surrounding the latter. There is merely determination of the chromophore concentration on the basis of the pilot light pulse, so that this concentration can be set appropriately beforehand, i.e before starting the treatment. The control unit can moreover be programed so that such a pilot light pulse can be emitted at regular intervals or, for example, before emitting each therapeutic pulse, in order to detect changes in the chromophore concentration in good time.
A computer unit then determines the chromophore concentration from a power of the pilot light pulse and the reflected light power, measured by the measuring unit, using the formula indicated above.
It may also be provided in one embodiment for the measuring unit to use its own measuring light source. The light from the measuring light source can be directed onto the therapy area, but with this embodiment there is also the possibility of directing the light from the measuring light source onto another body area on which the chromophore concentration in the patient""s blood can easily be measured.
It has proven advantageous in the control of the laser power for the latter to be controlled in inverse proportion to the chromophore concentration found. The product of the applied laser power and measured concentration therefore remains essentially constant during the treatment. The laser beam is preferably emitted in the form of pulses, preferably in the form of rectangular pulses with a duration not exceeding 10 ms, preferably with a duration of from 1 to 5 ms. The use of such short light pulses in conjunction with a relatively high power ensures that the therapeutic light can penetrate into the vessel and pass through the vessel, and the coagulation process induced by the heat is restricted to the vessel. In some applications, however, it has also proven advantageous to control the laser so that the pulses can be executed not as single pulses but as double pulses with a pause of less than 5 ms. A pause of less than 5 ms is below the thermal relaxation time so that the therapeutic effect of the second pulse is also still ensured. On the other hand, however, the pause allows interim cooling of the surrounding tissue, especially of the tissue located in front of the blood vessel, so that this mode of operating the laser has proven to be harmless to tissue.
In another advantageous embodiment of the invention, the control unit is designed so that the pulse length is controlled in a contrary sense to the power. This is because it has proven advantageous for vessel treatment if the pulse length is increased, for example if the power of the laser beam is reduced because of a high chromophore content, so that the total energy of a light pulse introduced into the vessel is kept approximately constant
The laser advantageously used is a diode laser with a power of from 100 to 800 watts and an emission wavelength of 805 nm.
In order to guide the laser light with great accuracy onto the patient""s vessels to be treated, an advantageous embodiment provides for the laser to be connected via a light guide to a handpiece. The hand-piece can have a transparent contact area for contact with the patient""s skin. It is also possible to provide in the handpiece, similar to a dermatoscope, an illumination unit and a magnifier, and a scale for measuring the vessels to be treated. The laser beam is guided into the dermatoscope-like handpiece by a spectrally selective mirror, preferably a dichroic mirror, it being possible for the therapist to observe the therapy area through the mirror from behind it. The therapist is able by means of an aiming mark, which is preferably attached on the transparent contact area, in the handpiece, to direct the laser beam specifically onto the vessel to be treated. The therapist is able to establish the size of the vessel by a scale in the handpiece.
An advantageous embodiment of the invention provides in the handpiece an adjustable aperture with which the diameter of the laser beam can be limited so that only the vessel is irradiated and irradiation of tissue beyond the margins of the vessel is avoided.
A particularly advantageous embodiment provides for the control unit to block emission of laser light by the laser when the chromophore concentration found by the measuring unit is below a preset lower threshold. Below a particular lower threshold of chromophore concentration it would be necessary for the power of the laser to be high to compensate for this low concentration, which would not be optimal for the therapy. The blocking of the device therefore avoids such inappropriate treatment in the region where the chromophore concentrations are too low.
Surprisingly, it has also emerged that a treatment may be insufficient if the chromophore concentrations are too high. A further advantageous embodiment of the invention therefore provides for the control unit to block emission of light pulses by the laser when the chromophore concentration found by the measuring unit is above a preset upper threshold. This is because it has been found that when the chromophore concentrations are too high the therapeutic laser light is absorbed so strongly that it is unable to penetrate sufficiently through the vessel to be treated. On the contrary, the laser light is absorbed exclusively on the margin of the vessel so that the coagulation does not extend over the complete vessel cross section, and the vessel thus cannot be sclerosed as desired.
A further advantageous embodiment of the invention provides an intensity sensor, which is preferably accommodated in the handpiece. The intensity sensor is able to measure the light reflected at the treatment site in order to determine the exogenous chromophore concentration. However, it is also possible, instead of accommodating the intensity sensor in the handpiece, to arrange an outcoupling mirror in the laser light path to pass reflected light to the intensity sensor. In this case, the intensity sensor can advantageously be arranged near the laser.
An advantageous embodiment is also one in which the handpiece is connected to a video camera. The therapy area can be displayed by the video camera on a monitor, in which case a false color display of the chromophore concentration facilitates the finding by the therapist of the blood vessels to be treated. In a further advantageous embodiment of the invention, the handpiece is provided with a cooling unit, preferably a Peltier element. This can remove the heat which is released during the treatment and frequently felt to be unpleasant by the patient.
Other features, characteristics and advantages of the present invention will become apparent from the following description of the invention, which refers to the accompanying drawings: